Surgical needles are well known in the surgical arts. Typically the surgical needles are mounted to sutures, and used in a variety of surgical procedures for approximating tissue. It is important that the surgical needles function under a variety of conditions encountered by surgeons when performing procedures on patients. Surgical needles can be used for delicate surgical procedures with relatively soft and fragile tissues such as liver or lung surgery and for more robust procedures involving harder and tougher tissues such as ophthalmic, plastic, or coronary artery bypass graft surgery. Surgical needles are also used in various orthopaedic surgical procedures. Surgical needles must be able to penetrate tissue rapidly and efficiently with minimal surgeon insertion force and minimal tissue trauma. It is particularly important that the surgical needle maintain its structural integrity through multiple cycles while tissue is being approximated by the surgeon.
Surgical needles may be made from a variety of materials that have the required strength and manufacturability properties. Examples of these materials include various grades of stainless steel including, 420, 455, 4310 and various grades of specialty martensitic-aged steels including ETHALLOY (Ethicon, Inc., Somerville, N.J.). Although needles made from such conventional materials are capable of adequate performance, there is a constant search for surgical needles having improved properties that will benefit both the surgeon and the patient. Certain refractory metals offer unique properties such as exceptional stiffness and strength that impart desirable handling characteristics to suture needles. However, the room temperature formability of many refractory alloys is limited and often substantially less than the formability of other metals typically used in the manufacture of suture needles. Difficulties may thus arise in the manufacture of refractory alloy surgical needles as numerous steps in a conventional manufacturing process require substantial material ductility. Suture needle bodies are often press-formed or coined to exhibit flattened sides to facilitate grasping and needle orientation within the suture needle drivers. Needle bodies formed to exhibit flattened sides may also impart modest improvements in strength and stiffness to the suture needle. Needle points also may be coined to produce cutting edges desirable for the penetration of certain tissues. Furthermore, needles are commonly curved into a variety of arcuate configurations, for example, ¼, ⅜, or ½ circle designs, in order to facilitate certain surgical procedures. The surgical needles must be processed during manufacturing to provide for the mounting of surgical sutures. One way of mounting sutures to a surgical needle is to drill a blind bore hole into the proximal end of the needle to receive the end of a surgical suture. For channel mounted sutures, as opposed to sutures mounted in a drilled bore hole in the proximal end of the needle, needle channels are typically coined or stamped into the proximal end of the suture needle. In either type of mounting configuration, the proximal ends of the needles are typically swaged to maintain the suture end in the channel or the bore hole.
The forming of refractory alloys into suture needle materials has not been extensively investigated. Conventional needle forming methods typically cannot be used with refractory alloys. For example, it is known to use a method of forming a suture receiving hole in steel needles by pressing a perforating tool into the base of suture needle while the needle material is heated to a temperature close to the melting temperature, Tm, between the hot forming and casting temperature of the alloy. This method is deficient for use on refractory metals for several reasons. If an alloy is taken to a temperature near the melting point of the alloy, recrystallization of the alloy is a distinct likelihood. Indeed recrystallization commonly occurs at much lower temperatures, for many alloys around 0.4 Tm. If refractory metals are heated to near their melting point, recrystallization of the work hardened microstructure occurs and the alloy can be expected to lose essential properties and even exhibit brittle characteristics at room temperature due to the effect of microstructural changes on the ductile to brittle transition temperature, DBTT. Secondly, such a process is applicable to oxidation resistant alloys, however, this is not the case for refractory alloys (especially those in the W—Re binary system) as these alloys will readily oxidize at temperatures far below their melting points.
The previously described needle forming methods may impart substantial stresses to the needle material, and if the material exhibits insufficient ductility, cracking and or splitting of the suture needle may occur. Many refractory alloys exhibit ductile to brittle transition temperatures (DBTT) above room temperature, and consequently the ability to plastically deform these refractory alloys in the various surgical needle forming operations is substantially limited. However, once above the DBTT, plastic deformability of the refractory alloys increases substantially. Excessively high temperatures may however lead to the recrystallization and growth of the grain structure of the alloy, leading to a substantial change in properties that may be deleterious to the performance of the suture needle.
Therefore, there is a need in this art for novel methods of manufacturing and forming refractory alloy suture needles.